One common application of thermal sensors is in thermal (infrared) imaging devices such as night vision equipment. One such class of thermal imaging devices includes a focal plane array of infrared detector elements or thermal sensors coupled to an integrated circuit substrate with a corresponding array of contact pads between the focal plane array and the integrated circuit substrate. The thermal sensors define the respective picture elements (or pixels) of the resulting thermal image.
One type of thermal sensor includes a ferroelectric or pyroelectric element formed from ferroelectric material which exhibits a state of electrical polarization dependent upon temperature changes in response to incident infrared radiation. An infrared absorber and common electrode are disposed on one side of the ferroelectric elements. A sensor signal electrode is disposed on the opposite side of each ferroelectric element. The infrared absorber and common electrode extend across the surface of the focal plane array and are attached to each of the ferroelectric elements. Each ferroelectric element generally has its own separate sensor signal electrode. Each infrared detector element or thermal sensor is defined in part by the infrared absorber and common electrode and the respective sensor signal electrode. The electrodes constitute capacitive plates and the ferroelectric element constitutes a dielectric or insulator disposed between the capacitive plates.
Thermal isolation structures are typically disposed between the focal plane array and the integrated circuit substrate to provide both mechanical bonding and a sensor signal flowpath while minimizing thermal diffusion from the respective thermal sensors to the integrated circuit substrate. Several approaches have been used to provide such thermal isolation structures for isolating an array of thermal sensors from an underlying integrated circuit substrate. Examples of such thermal isolation structures are shown in U.S. Pat. No. 4,143,269 entitled Ferroelectric Imaging System to McCormack, et al., and U.S. Pat. No. 5,047,644 entitled Polyimide Thermal Isolation Mesa for a Thermal Imaging System to Meissner, et al., both assigned to Texas Instruments Incorporated, the assignee of this invention.